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It is no secret that South Korea inhabits a dangerous neighborhood, and the question of whether it can defend itself against key foreign threats looms large. The impending personnel shortages precipitated by the country’s mounting demographic challenges must be addressed head on to prevent these difficulties from eroding the country’s national defense posture.

South Korea doesn’t need nor can it afford another round of defense reforms that results in only marginal changes. The next government, which will enter office in May 2021, must undertake bipartisan defense reforms that look into long-term conflict drivers and likely scenarios; modernize and revamp military training, education, and doctrines; maximize interoperability with U.S. forces; ensure greater joint warfighting capabilities; and lay the foundation for intensified U.S–South Korea defense technology cooperation.

South Korea’s Changing Military

South Korea’s armed forces are shrinking. To offset the military’s dwindling supply of soldiers, the country is reforming its forces to accommodate a necessary reduction from a 599,000-strong force to a size of 522,000 troops by 2022. This figure includes both conscripts and volunteer forces. Out of this 522,000 figure, the military hopes to keep a baseline number of 274,000 conscripts—the number the Ministry of Defense deems necessary to sustain a conscript force large enough to accomplish its objectives. According to media reports of the South Korean Ministry of National Defense’s views, the pool of draftees, which South Korea relies on for nearly half of its total military force, is going to decline “by nearly half over the next two decades.” The forecast of South Korean men that will enlist for their mandatory military service each year—based on the number of twenty-year-old men each year, a typical age for conscription—is slated to fall from 330,000 at the end of 2020 to about 240,000 by 2036, and then the figure is expected to drop further to around 186,000 by 2039. Hence, the South Korean military will face a progressively worsening personnel deficit from the mid-2020s onward if it plans to maintain a baseline force of some 274,000 conscripts in its 522,000-strong force (see figure 1). Presumably, these demographic trends will also somewhat affect the number of volunteers the military is able to secure.

Demographics are not the only changes that South Korea’s armed forces are experiencing. The country’s military is also transitioning to more technologically advanced platforms, downsizing its ground forces, and recruiting more civilian experts. Yet these efforts, while important, have not been enough.

Since North Korea’s army has about 1.1 million ground troops and the bulk of them are located near the Thirty-Eighth Parallel, the South Korean military rightly has focused historically on ground forces. But with North Korea now armed with nuclear warheads and wide-ranging ballistic missiles, including sea-launched ballistic missiles, South Korea’s armed forces must be reconfigured to meet a growing array of asymmetrical threats. Meanwhile, China’s anti-access area-denial capabilities—including sophisticated anti-ship missiles and growing air and naval power—could significantly constrain, deter, or even deny the possibility of coordinated U.S.–South Korean and/or U.S.-Japan military operations in acute crises or wars. Seoul can no longer ignore North Korea’s growing capabilities or China’s relentless military rise.

Chung Min Lee
Chung Min Lee is a senior fellow in Carnegie’s Asia Program. He is an expert on Korean and Northeast Asian security, defense, intelligence, and crisis management.
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As the South Korean military grapples with how to mitigate an increasingly acute personnel shortage, it is placing a greater emphasis on air and naval forces that will enable greater operational depth, including long-range ballistic missiles and (circumstances permitting) even nuclear-powered submarines. Such moves are necessitating doctrinal modernization that prioritizes air and naval forces with increasingly complex deterrence and defense mission assignments.

Granted, it is not all about air and naval forces, but they are very strategically important. It would be naïve to assume that a future conflict on the Korean Peninsula could be won primarily by air and naval forces. After all, if North Korea were to stoke another war on the peninsula, South Korean ground forces would still play a central role in mounting counteroffensives. Even so, overarching victory for South Korea could only be assured by achieving air superiority, controlling critical sea lanes, and undertaking unparalleled joint operations.

In the last year of President Moon Jae-in’s administration, significant movement on any of these fronts will be increasingly difficult due to the term-limited president’s waning political influence. All eyes are on the critical March 2022 presidential election, since the ruling party is not going to use its political capital before then to push through massive defense reforms. But regardless of which party wins the presidency, South Korea can ill afford to continue expensive, piecemeal, and service-dominant defense reforms or politically motivated measures (such as downsizing and downgrading military exercises to help foster inter-Korean détente). Unless South Korea’s political and military leadership implements military reforms akin to the massive restructuring of the South Korean economy following the 1997–1998 Asian financial crisis, the military (and especially the army’s leadership) will likely return to its favorite tactic of piecemeal reforms. The South Korean military is increasingly operating advanced weapons systems due to shortages in military personnel and an evolving threat environment. But ultimately, the armed forces will only be as good as its personnel.

The South Korean Military’s Two Major Challenges

Viewing national security more holistically to include economic growth projections and fiscal constraints, it becomes clear that South Korea must cope with twin demographic time bombs. First of all, the rapidly rising costs of caring for an aging population will likely create pressure to curtail defense spending. And second, the looming shortfall of South Korean troops on the horizon will do nothing to improve matters.

On the first point, with a shrinking population that is rapidly aging, South Korea’s social welfare and healthcare costs are poised to sharply increase and potentially constrain the country’s defense spending. According to the OECD, public social welfare costs accounted for 12.2 percent of South Korea’s $1.6 trillion GDP in 2019. The country’s 2019 healthcare costs amounted to 8 percent of GDP. While South Korea spent only about half what the average OECD member did on social welfare in 2018 (11.1 percent versus 20.1 percent), the country’s Ministry of Health and Welfare stated, “with an aging population and low economic growth, social welfare spending is going to increase to about 20.1 percent [of GDP] by the late 2030s and, by 2060, it is expected to account for 28.6 percent [of GDP].”

Meanwhile, South Korea allocated about $48 billion for its 2021 defense budget, or about 9.4 percent of government spending and roughly 2.9 percent of the country’s $1.6 trillion GDP (according to the author’s calculations). However, while the Moon administration has continued to increase the defense budget during its tenure, the ratio of defense spending as a percentage of GDP is highly unlikely to keep growing, given the country’s sharp projected increases in social welfare and healthcare spending.

Second of all, even with all of the defense reforms South Korea has undertaken over the past two decades and the blueprints for further potential reforms throughout the 2020s, the armed forces’ expected personnel shortages and related challenges are likely to persist. The Ministry of National Defense asserts it can cope with significant manpower shortages by transforming the military into a high-tech force, recruiting more civilian specialists, and implementing ongoing force rationalization measures (such as reducing the country’s ground forces to 522,000 in 2022 and recruiting more noncommissioned officers (NCOs). NCOs are vital to ensuring top-level training, management, and leadership throughout the services, especially with the planned downsizing of the officer corps following the continued reduction of South Korean military units.

With only one year left in office, Moon is highly unlikely to focus on military manpower reforms given the enormous efforts that are required. That said, critical changes are long overdue to address rampant sexual harrasment in the armed forces. South Korea’s air force chief resigned in early June 2021 to take moral responsibility for a case involving a female NCO who unfortunately committed suicide following months of inaction by the air force after she reported repeated assaults.

Despite the South Korean government’s and armed forces’ claims that critical defense reforms are being implemented, doubts persist. As noted above, South Korea will face much bigger security threats throughout the 2020s and the 2030s. China’s growing military footprint and growing ability to significantly curtail or even deter South Korean military operations is making Seoul’s security environment tougher with each passing year.

Hence, strengthening South Korea’s air and naval forces and procuring more sophisticated ballistic missiles (including sea-launched ones) will become increasingly critical. But one of the main sticking points is the South Korean navy’s inability to recruit key manpower such as NCOs for long-term duties. For example, in the last decade, due to shortages of personnel tasked with active sea duty, the navy has reallocated 3,700 personnel stationed at naval facilities and bases from land duty to active sea duty, but even with these changes the navy’s personel levels for sea duty still fall 3,000 short. Such naval personnel must be highly skilled, yet many recruits are reluctant to sign up for sea duty given the high demands of life at sea for extended periods of time.

In response to this personnel shortfall, the Ministry of National Defense is contemplating several policies, including the possibility of a gradual shift to a volunteer force. Advocates argue that such a move would help mitigate youth unemployment in the country. Opponents assert that a voluntary force would result in exponential cost hikes. According to figures from a 2019 study by the National Assembly’s Budget Office, a full-on move to a volunteer force between 2021 and 2025 would cost approximately $26.1 billion, while maintaining a conscripted force over the same period would cost just more than half that ($14.2 billion). Again, given South Korea’s sharp projected increases in social welfare spending and healthcare costs and other nonmilitary outlays such as education and housing, securing around $2.4 billion in additional funds each year for five years for the military’s personnel budget would be extremely difficult.


Ultimately, South Korea’s ability to cope with its hugely disruptive and expensive demographic transitions—including in the armed forces—demands an all-of-government response and nationwide reforms. So far, successive governments on the left and the right have not linked the civilian and military effects of the country’s demographic transitions. But among all of the tasks that the next government will face, nothing is arguably more important than putting into place a bipartisan national demographic transition policy with corresponding budgets and policies.

There is still time for South Korea to address the policy challenges of a shrinking and aging population. However, Seoul has to fundamentally rethink how it will retain, or even strengthen, its national security posture. For the future of South Korean national security, nothing is more important than shifting away from an army-dominant organizational culture and related policies by way of bold defense reforms. And equally important, all of the country’s major political parties must agree not to politicize bipartisan defense reform measures.